i rechecked. it's set to HS. tino 2007/12/20, PAUL James : > > > Make sure you have the "HS" oscillator option chosen. You probably do, > but just making sure. > > > > Jim > > -----Original Message----- > From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf > Of Bob Axtell > Sent: Wednesday, December 19, 2007 4:59 PM > To: Microcontroller discussion list - Public. > Subject: Re: [PIC]: 16F877 oscillator does not work at 20MHz > > tinu b wrote: > > i'm about to debug my ICD2 clone, i bought as a kit some time ago. > > it is based on a 16F877-20 and has a 20MHz xtal with 22pF load > > capacitors attached. > > > > i found that the oscillator is not working. > > i checked the fuses: the pic is configured for HS, so i think this is > ok. > > > > a replaced the xtal, i replaced the load capacitors with different > > values, no chance. > > > > when i replace the xtal with a 10MHz version, the oscillator works. > > but as soon as i put back a 20MHz one, there's no oscillation. > > > > what shall i do? > > any idea? > > > > thanx in advance! > > tino > > > First of all, the 16F877 doesn't have the ICD2 debug unit built into > it. You need the 16F877A . > > Second, it is almost impossible to actually be certain that a 20M > crystal is oscillating on frequency. > > Make certaain that the F877 is properly bypassed; a 0.1uF ceramic is > correct if the leads to the VDD and GND pins are fat enough. Some > crystals are cranky at 20M and will not work properly on some PICs; > especially crystals from ECS. Try a cylindrical crystal from EPSON > TOYOCOM; they are outstanding crystals and work well with PICs; I've > never seen a failure. > > The 877 and the 877A both use two VSS (GND) and two VDD pins. Make sure > all 4 are connected properly. If one pin floats, strange, "X-file-like" > effects happen. > > --Bob > -- > http://www.piclist.com PIC/SX FAQ & list archive View/change your > membership options at http://mailman.mit.edu/mailman/listinfo/piclist > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist